Leaders in Toxic Releases : Pollution: Four firms produced 95% of air emissions around Glendale in 1990. The overall amount declined 10% in Southern California, but rose 6% in Glendale.

In the San Fernando Road industrial area, a Glendale company makes rubbery materials to seal aircraft fuel tanks and skyscraper windows. Last year, the firm, Products Research & Chemical Corp., released 162,974 pounds of toxic chemicals into the skies above Glendale and surrounding Los Angeles.

Not far away, on the Los Angeles side of San Fernando Road, Philips Components, a factory that produces ceramic capacitor chips for the circuitry of automobile heaters, radios and televisions, last year vented 150,098 pounds into the air.

A printing plant nearby in Los Angeles, Bertco Graphics on Glendale Boulevard, accounted for 75,600 pounds more. And Nelson Name Plate, a Casitas Avenue factory that stamps out manufacturers' metal identification plates--placed on products as diverse as dishwashers and sailboat masts--added 139,479 pounds of toxic air emissions.

These four firms were responsible for 95% of the total air emissions in Glendale and the Northeast Los Angeles neighborhoods, according to annual reports the companies filed with the federal government last summer.

The businesses, along with nine other firms, released 554,871 pounds of toxic air emissions, or slightly less than 2% of the Los Angeles County total.

Some of the toxic compounds cause smog. Some deplete the Earth's protective ozone layer. Some are believed to cause cancer and reproductive harm in humans.

However, beyond those broad conclusions, industrial, scientific and environmental experts say it is impossible to pinpoint what immediate and precise health effects occur from the release--in the course of manufacturing processes--of tons upon tons of chemicals in the region.

"The real story is told by exposure," Robert Pease, planning manager for the air toxics division of the South Coast Air Quality Management District, said of health risks. The inventory does not measure exposure.

Complex factors contribute to air pollution risks, he said, including meteorology and the concentration and dilution of chemicals. Also, the Glendale area does not exist in isolation but is part of the larger Los Angeles Basin. Chemicals in the air migrate from place to place in Southern California.

Air experts say it is known, however, that manufacturing pollutants, along with other sources such as power plants, account for 20% of the region's smog. Automobile and truck traffic is blamed for even more--50%.

The requirement to file the toxic emission reports is based on a federal "community right to know" law passed in 1986 by Congress in reaction to the chemical disaster at a Union Carbide plant in Bhopal, India. Two thousand people died there and 200,000 more were injured.

The annual pollution inventory is by no means perfect, said Hacienda Heights environmentalist Wil Baca, who is a board member of the Coalition for Clean Air, but he said it has helped to keep companies more environmentally honest.

"It does put them on notice that they've got to discipline themselves to reduce the use of toxics," he said.

The 1990 Southern California air emission figures--drawn by The Times from the annual reports filed last summer with the U.S. Environmental Protection Agency--do, in fact, reflect a continuing downward trend. The totals dropped by 10%.

However, whereas the overall total of Los Angeles County dropped 14%, 13 Glendale and neighboring Los Angeles manufacturers bucked a nationwide and regional trend last year by reporting a slight increase--6%--in the total amount of toxic chemicals they legally vented.

Air experts attribute this partly to the growth of a few individual Glendale area businesses, such as Nelson Name Plate.

Still, Robert Pease said "generally, we're seeing a downward trend, and we think that is a positive trend."

Government officials, scientists, environmental activists and industry representatives attribute the decline to a combination of factors.

These include the overall economic slowdown and companies' fears of adverse pollution publicity combined with their desires to appear as environmental "good neighbors."

In addition, the decline is attributed to the movement away from the use of toxic chemicals, owing partly to the federal Clean Air Act and to increasingly strict regulations of the local air district, which is extracting higher and higher permit fees for the manufacturing use of certain chemicals.

From large companies to small, local executives stressed that they are doing what they can to cut down on toxic chemicals. Furthermore, they said that within the next few years, and certainly within the coming decade, they will have found alternatives for many toxic compounds and converted away from solvent-based cleaning agents, degreasers, paints, adhesives and sealants.

At Nelson Name Plate, founded locally in 1946, the change is coming gradually, company President Tom Cassutt said.